There are as many as 300,000 coronary bypass graft procedures performed annually in the United States. Each of those procedures may include one or more graft vessels. Currently, each graft vessel must be hand sutured. As many as four or more grafts are placed in a procedure. Until recently, coronary artery bypass procedures have been performed with the patient on cardiopulmonary bypass whereby the heart is stopped with cardioplegia and the surgery performed on an exposed and still heart.
Some pioneering surgeons are performing procedures in which the coronary bypass is performed on a beating heart. That is, without heart-lung bypass and cardioplegia. This minimizes the time it takes to perform the procedure and reduces the cost of the operation by eliminating the heart-lung bypass machine.
Coronary Artery Bypass Grafting (CABG) is performed and a new blood supply to the heart muscle is established when coronary arteries are blocked with calcium or plaque. A new blood supply conduit is joined to the diseased coronary, distal to the blockage, thus providing a fresh supply of oxygenated blood to the vessel in question. Today, this is accomplished by hand suturing a graft vessel (the new supply of blood) to the diseases vessel. This junction is called an anastomosis of vessels. Many different types of supply conduits can be used. Examples are cadaver vein, saphenous vein, radial artery, internal mammary artery, and the like.
By way of background, the basic operation of a heart will be briefly discussed. The hear works like a pump. The left and right ventricles are separate but share a common wall (the septum). The left ventricle is thicker and pumps the blood into the systemic circulation. The work it performs is much greater than the right ventricle. The right ventricle pumps blood into the pulmonary circulation, which is a low pressure circuit. The left ventricle wall (a low energy system) is much thinner than the right ventricle.
The left ventricle fills in diastole and ejects in systole. The difference between the diastolic volume (largest) and the systolic volume (smallest) (the stroke volume or amount of blood ejected on each heartbeat) multiplied by heart rate determines the cardiac output of the heart (liters/min. of flow). The heart shortens during systole as the muscle contracts. There are a number of motions during contraction (including a considerable amount of rotation) but for practical purposes the heart can be though of as a truncated cone. Shortening occurs along its length and also along its diameter. For purposes of this disclosure, the more important of the two motions is the shortening along the diameter since the ejection volume varies as the square vs. along the length which varies with the first power.
The heart functions well whether the person is upright, upside down, prone or supine. It sits inside the pericardium—a sac which limits its motion and spreads the support on the heart so that no matter how a person position himself, it is not particularly compressed and is able to fill and then eject with each heartbeat. The concept of the pericardium spreading the load is critical, i.e., when lying supine, the posterior pericardium supports the heart over a large surface of the heart just as when the person is lying on his stomach, the front of the pericardium spreads the load.
When the chest is opened by a median sternotomy it is possible to gain access to all chambers and surfaces of the heart. This combined with the fact that this incision is usually less painful than a thoracotomy (rib separation), makes this the preferred surgical approach to the heart.
The coronary vessels are surface vessels, only occasionally dipping into the myocardium making them accessible without opening the heart. Traditionally, bypass surgery is done with the heart arrested. This stops the motion of the heart and allows the arrest of the coronary circulation so the surgeon sews in a bloodless and easy to see field. Since the heart is stopped, the patient would suffer irreversible damage to the brain and other tissue and organs without the use of the heart-lung machine to support the general circulation. Although the heart-lung machine has been refined, it is particularly toxic to older and debilitated patients and it is expensive.
It is possible to perform surgery off bypass, while the heart is beating and the coronaries are under positive blood pressure; however, there may be problems. One problem is that not all vessels are accessible wince some vessels are on the posterior or inferior surfaces and that when such vessels are brought into view by lifting the heart, cardiac performance is impaired such that the cardiac output falls and blood pressure drops. A second problem is that the heart moves so that suturing in vessels (12 to 15 stitches in a vessel under 2 mm in diameter) might be inaccurate and a third problem is that there is blood in the field as the coronary circulation is not interrupted. This last problem is now largely solved by snares, which temporarily stop the flow of blood through the targeted arteries. The problem of lifting the heart is not to impair the performance of the heart while at the same time adequately exposing the heart and regionally immobilizing a vessel during beating heart surgery, and this problem is not solved with any prior art system.
Therefore there is a significant need for a means and a method for lifting a heart so as not to impair the performance of the heart while at the same time adequately exposing the heart and regionally immobilizing a vessel during beating heart surgery.
Lifting of the heart is deleterious to heart function for several reasons. First, the lifting of the heart impairs the venous return to the heart so that there is less diastolic filling of the heart (this can largely be corrected by putting the head down and the feet up to increase venous return). Second, the heart is distorted. Using a hand or spatula to lift the heart is quite different than simply changing body position when the heart is inside the chest. The force of the hand on the heart is localized so that the heart is no longer a truncated cone, but is much flatter. This shape is much less effective for ejection (the circle is the most effective as it has the highest ratios of volume to diameter) and flattening also limits the diastolic volumes so that inadequate filling occurs.
In order to perform cardiac surgery on a beating hart, there is a need to lift, support and orient the heart without reducing its ability to function. The inventors have discovered that the secret is to work like the pericardium does when a person changes body position and do everything possible to keep the heart's shape consistent.
In coronary bypass operation, grafts have to be anastomosed to the anterior descending artery (right coronary artery branch), the circumflex artery, and to the posterior descending artery. The anterior descending artery lies on the front surface of the heart and is easily accessible to the surgeon without particular help from surgical assistants or using any devices. The circumflex and posterior descending arteries, however, lie on the back surface of the heart. Therefore, to expose the circumflex artery to a field of view of the surgeon, it is mandatory to lift the heart and rotate it about the axis of the inferior vena cava and the superior vena cava. Likewise, to expose the posterior descending artery, it is necessary to lift the heart and rotate it in the direction of its apex. If the heart is moved improperly, it may go into fibrillation.
Ordinarily, a surgical assistant is employed to lift the heart by using his or her hand, this is satisfactory for an arrested heart. However this is not satisfactory for a beating heart. However, it is very difficult and tiring to keep the heart in a steady position. Furthermore, the myocardium in contact with the assistant's fingers may be damaged by pressure, avulsion, and premature rewarming. Further, the assistant's hand in the operative field can get in the way, and the assistant, who often stands next to the surgeon may restrict the surgeon's movements.
Therefore there is a need for a heart retractor which will support the heart in position for coronary bypass surgery of the circumflex coronary artery and posterior descending artery.
Another prior art method of supporting a heart is by use of a sling. A sling is a network of fabric or plastic that is placed around the heart in the manner of a hammock. The heart is then supported by the sling. It is noted that in order for a sling to work as a retractor, the surgeon is required to arranged the ties to be pulled form the proper direction, such as normal to the desired direction of lift, which can be onerous. This presents a serious problem since there are no easy reference points above the patient in which to attach these ties.
While the art has included several inventions intended to support the heart during coronary bypass surgery of the circumflex coronary artery, these inventions have several drawbacks that have hindered their acceptance in the art. For example, the use of nets to support the heart exposes the heart to fine strands which impinge on the heart and may cause damage. Furthermore, nets may impede the surgical target and require special techniques or procedures to remove the net form the surgical target area. This is especially onerous in the net mesh is fine. Flat cloth tapes are a form of net, and may damage the heart due to a rough texture of the cloth and the small area of contact between the tape strands and the heart. Further, tapes and similar devices that do not have large surface areas contacting the heart may not support the heart in a uniform manner and may create large pressure areas at the contact points.
Therefore, there is a need for a heart retractor which will support the heart in position for coronary bypass surgery of the circumflex coronary artery in a manner that will not damage the heart yet will provide easy access to the surgical target and will keep working while cardiac output is maintained.
A further consideration in coronary artery surgery is hemorrhage from the incision into the coronary artery at the proposed anastomotic site. Therefore, heretofore, coronary artery surgery has been carried out under conditions of cardiac arrest and aortic root cross clamping. Hence, the myocardium is temporarily deprived of coronary blood supply. In some patients, an additional coronary blood supply, through the form of bronchial circulation, cause significant hemorrhage during the bypass grafting process. This hemorrhage is inconvenient, as it masks the surgeon's view during the delicate suturing process, and threatens the well-being of the patient. Performing surgery in this manner has several additional drawbacks, including the need to stop the heart, the need to insert special equipment and procedural steps to carry out the function of moving blood through the patient's body while the heart is stopped.
Still further, there is a need for a heart retractor which permits regional as well as specific immobilization of the heart.
However, the continued operation of the heart will produce problems, in addition to the above-discussed problems, of forming a moving target for the surgeon. That is, since the heart continues to beat during the operation, the surgical target will move in connection with such beating movement. The heart cannot be stopped or unduly constrained without increasing the danger of fibrillation.
Therefore, there is a need for a heart retractor which will support a beating heart in position for coronary bypass surgery of coronary arteries in a manner that will not damage the heart yet will provide specific and regional support while allowing unabated cardiac output.
Recently, there has been interest in minimally invasive coronary bypass surgery. This is not surprising since a median sternotomy and a run on the cardiopulmonary bypass pump are not well tolerated by some patients, combined with the added cost of coronary bypass equipment and staff. The procedure results in considerable recovery time and is associated with a risk of death and major complication. While the ultimate goal is to provide bypass to all vessels by port access (like gallbladder surgery) and to eliminate the need for cardiopulmonary bypass, a more limited but reasonable option for the next number or years will be to perform bypass off pump with an incision (sternotomy or thoracotomy). A tool which could allow performance of multivessel off pump bypass would be most helpful.
Therefore, there is a need for a heart retractor which will support the heart in position for minimally invasive coronary bypass surgery of coronary arteries, including the circumflex coronary artery, in a manner that will not damage the heart yet will provide easy access to the surgical target without requiring the heart to be stopped yet without unduly constraining the heart.
Still further, the inventors have observed that not all hearts are the same size, shape and have the same spacing between corresponding areas. Thus, while all hearts are basically the same, there may be a variation between individual hearts. Therefore, a device that supports a heart should account for these variations. This is especially true if the heart is to continue pumping during the operation and while it is supported. If the support is not fit to the particular heart, it may constrict the heart in some manner and thus interfere with the continued output of the heart.
Therefore, there is a need for a heart retractor which will support a heart, especially a beating heart, during coronary surgery and which can be adjusted to fit the particular needs of the individual heart and will support the heart both in gross and regionally.